Vol. 1] Clausen. — Lifc-Historics of California CoccinelUdae. 263 



Hippodamia convergens Guer. 



The twelve-spotted eoccinellid {H. convcrgens) is very gen- 

 erally distributed throughout the state and is by far the most 

 important member of the eoccinellid group as regards aphis con- 

 trol by natural means. This species is shipped by the millions 

 into Imperial Valley each spring for the purpose of combating 

 the melon aphis {Aphis gossypii) . During the late summer and 

 fall months the adult beetles gather in great colonies in moun- 

 tain caiions and other cool and protected places, and may be 

 found in great quantities among the dead leaves and brush or 

 clustered upon rocky surfaces. 



The aphids upon which this eoccinellid feeds are extensive in 

 number, but the main species infesting cultivated plants are the 

 hop aphis {Phorodon humuli), the rose aphis {Macrosiphum 

 rosae), the beet louse (Pemphigus hetae), the oleander aphis 

 (Aphis nerii), the bean aphis (Aphis rumicis), the plum aphis 

 (Hyalopterus arundinis), and the melon aphis (Aphis gos- 

 sypii). Feeding has been observed to a comparatively limited 

 extent upon the walnut aphis (Chromaphis juglandicola), the 

 woolly apple aphis (Schizoncura lanigera), and the cabbage 

 aphis (Aphis hrassicae) . The elm aphis, though very numerous, 

 was very seldom attacked. 



The Egg. — The eggs of H. eonvergens are 1.4 mm. long, 

 spindle-shaped, and bright yellow in color, and are deposited ver- 

 tically in groups of ten to thirty on the under sides of leaves and 

 in other sheltered and protected places. A short time previous 

 to the time of hatching, the egg loses its bright yellow color and 

 assumes a grayish tint. The emergence of the young larva ordi- 

 narily takes place in the course of the day during whicli this 

 change occurs. In the great majority of cases all the eggs of a 

 given cluster will hatch within the period of one hour, but occas- 

 ionally the intervening period may be considerably longer, in 

 which case the larva tirst emerging may devour the contents of 

 the remainder of the cluster. 



In order to determine the approximate percentage of fertile 

 eggs among the total deposited four hundred were collected from 

 the foliage of a prune tree and an accurate count made of the 

 emerging larvae. A total of 332, or 83 per cent, was secured. 

 Of those failing to hatch, a few Avere broken by young larvae, 



